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Home > Help Needed / General Tech Chat > GT17 - too much boost

85-mayfair

8 Posts
Member #: 11596
Junior Member

Kent

Hello everyone,

I've just put together my first turbo build - it's a 998 with a new chinese GT17, running on a SC 5 port EFI kit. Now it's up and running, but I seem to have come up against a problem which I can't easily find the answer to. The actuator that came with the turbo only starts to operate at 17psi, and I was aiming to run 10psi. It seems odd because from what I have read, it should be set for around 5psi which can be overcome with a bleed valve. The actuator looks to be crimped together and I don't really fancy my chances of opening it up and getting the diaphragm to seal again. Is there a solution which doesn't involve buying an expensive actuator?

PS. Thanks to everyone on this forum - I would never have made it this far without the wealth of knowledge available on here.


robert

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uranus

check the pre load ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM


85-mayfair

8 Posts
Member #: 11596
Junior Member

Kent

How should it be set? When I fitted it, I did it so it only just held the little poppet valve shut. So the rod wasn't exactly tight to fit on the turbo. When I test the actuator with mityvac, the actuator rod only just starts to move at 17psi. I've only just taken it down the road for the first time tonight - only to put fresh petrol in it really, the map is nowhere near right - and when the boost came on I very quickly saw around 15psi on the gauge


wil_h

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Betwix Harrogate and York

Where is the feed for the actuator being taken from?

Is there a leak in the actuator hose?

Is the pipe and take-off of a reasonable size?

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

On 2nd Jan, 2013 fastcarl said:

the design shows a distinct lack of imagination,
talk about starting off with a clean sheet of paper, then not bothering to fucking draw on it,lol

On 20th Apr, 2012 Paul S said:
I'm mainly concerned about swirl in the runners caused by the tangential entry.


Sprocket

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Preston On The Brook

If your Mitty vac is showing 17psi at the point it starts to move the pushrod with the actuator on the bench, I’d say the actuator is faulty or the wrong one for the turbo.

Normally there is about 1.5 to 2mm pre load on the actuator, what that means is the amount you need to pull on the pushrod to get it to fit into the pin of a closed wastegate arm.

Some people increase the preload to increase the pressure at which the actuator starts to open.

On 26th Oct, 2004 TurboDave16v said:
Is it A-Series only? I think it should be...
So when some joey comes on here about how his 16v turbo vauxhall is great compared to ours, he can be given the 'bird'...


On 26th Oct, 2004 Tom Fenton said:
Yep I agree with TD........


TurboDave16V
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***16***

SouthPark, Colorado

It could simply be this is way too strong of an actuator.
With a set of pliers, A moderate grip and pull should be needed to pull the actuator rod, But an actuator set to 1.5 bar, would need a strong grip and Strong pull. If in any doubt, just buy a new actuator off eBay… They aren’t that expensive.
There are many different options for the angle of the hose tail versus the mounting bolts however, so figure out what you want Before you go searching...

On 17th Nov, 2014 Tom Fenton said:
Sorry to say My Herpes are no better


Ready to feel Ancient ??? This is 26 years old as of 2022 https://youtu.be/YQQokcoOzeY



Steve220

238 Posts
Member #: 11017
Senior Member

Shropshire

take off the actuator arm from the exhaust housing and you're looking for half a hole for pre-load.


wil_h

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Betwix Harrogate and York

ok. I might have one of these actuators spares as I've used a few Chinese GT17s but never used the actuators.

No promises though, I might have chucked them in the bin, will check later.

will be FOC, so don't panic.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

On 2nd Jan, 2013 fastcarl said:

the design shows a distinct lack of imagination,
talk about starting off with a clean sheet of paper, then not bothering to fucking draw on it,lol

On 20th Apr, 2012 Paul S said:
I'm mainly concerned about swirl in the runners caused by the tangential entry.


85-mayfair

8 Posts
Member #: 11596
Junior Member

Kent

Thanks everyone. I went back to it yesterday and checked it over again. The pipe is a decent bore and done up tight at both ends, I ran it from the fitting on the compressor housing which was how the turbo was set up when it arrived. I'm sure you're right and the actuator is just wrong - it just seemed odd! Everywhere I searched said these saab turbos were set for around 5psi. Maybe I put too much faith in Chinese turbo manufacturers.

Thanks Wil, although I think I should be sorted now. I bit the bullet and ordered one from ebay which claims to open at 5.4psi. Hopefully it will arrive today and just work with a bleed valve. I was aiming to take this car to Brooklands on Sunday so it's a race against time to do this, sort the map out and finish all the other little bits on the car


D4VE

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lowestoft suffolk

And what does said mini look like so i can spy it on sunday?

On 24th Oct, 2015 jonny f said:
Nothing gets past Dave lol

NOTHING GETS PAST ME!! *tongue*

1/4 mile 14.7 @ 96mph 12psi boost
Showdown class A 2nd place 18.6 @ 69mph


85-mayfair

8 Posts
Member #: 11596
Junior Member

Kent

Well I bought an actuator for a T3 from ebay. Description said it opened at 5.4psi so I thought perfect. It looked physically the same in the pictures. Turns out it's actually quite a bit bigger than the GT17 one so a bit of modification to my actuator bracket was in order - oops. Anyway sorted that out and set it with approx 1/2 a hole pre-load (I say approx because it's a little difficult to tell when the engine's in and you're looking down on it). Took it out tonight for about 2 hours of mapping and it seems to be perfect as it is - I'm seeing a maximum of 10psi on the gauge. Maybe I set the pre-load a little tight? I don't know.

Sorting the fuel map out is a completely different ball game it must be said. I started with a turbo base map that specialist components sent me, and in fairness they did say it wouldn't have been for a 998 engine. But whatever it was it must have been a totally different animal to my engine. I would have been better off tipping petrol down the manifold with a watering can. I've managed to get it driving okayish so far and I would be happy to get it to Brooklands after some more fettling (and sorting an oil leak from the timing cover area). However if anyone has a cal file for a 998 turbo, or even a picture of what the base maps look like, I would be very grateful!!

Dave, here is a picture taken last year on the way to the Ireland IMM which was basically it's last outing before I started the turbo project. It's looking a little ropey these days so if you do spot it, it is best viewed from a distance of about 20ft! *hehe!*


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Tom Fenton
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15300 Posts
Member #: 337
Fearless Tom Fenton, Avon Park 2007 & 2008 class D winner

&

TM legend.

Rotherham South Yorkshire

To be honest chap if you've got it running and driveable I'd spend the time refining what is there rather than trying any other base map. Base map is a grand term for an educated guess to be honest and the chances are that any other base map will be worse than what you have got to already.


On 29th Nov, 2016 madmk1 said:


On 28th Nov, 2016 Rob Gavin said:
I refuse to pay for anything else


Like fuel 😂😂


85-mayfair

8 Posts
Member #: 11596
Junior Member

Kent

I take your point. I have got it driving reasonably and it's safe enough until it gets to the rolling road. Seems to be on the rich side, except for the moment I press the accelerator. Pulling away is a pain. It goes lean for a second or two then picks up, and I am struggling to improve it. The 'acceleration multiplier' seems to make little difference whatever I do with it and doesn't make sense to me. In every base map I have, all the numbers in that table are well below zero. Surely if it is a multiplier to richen the mixture when you press the accelerator, they need to be above 1, to increase the final injection pulse width? I was going to ring specialist components this afternoon and ask a few questions but it seems the part timers go home at 12 on Fridays!!


Tom Fenton
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15300 Posts
Member #: 337
Fearless Tom Fenton, Avon Park 2007 & 2008 class D winner

&

TM legend.

Rotherham South Yorkshire

I can’t help you much as when I briefly had a mess with the SC ECU software I found it awful to use and difficult to make it do what I wanted.


On 29th Nov, 2016 madmk1 said:


On 28th Nov, 2016 Rob Gavin said:
I refuse to pay for anything else


Like fuel 😂😂


85-mayfair

8 Posts
Member #: 11596
Junior Member

Kent

Well, I don't have anything to compare it to, but I am inclined to agree! It often seems to glitch out and just refuse to accept the values you put in. Or you'll enter a value into a cell and it will change it, but not quite to the value you entered. I'm hoping the rolling road operator is going to have more success with it than me.

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